Introduction: The banking industry is considered one of the most important pillars of any economy, and due to the provision of various financial and credit services, it plays a crucial role in economic development. Considering the importance of efficiency in banks, it is necessary to identify the variables and ratios affecting the efficiency of banks. Thus, some factors such as fixed capital price, labor price, interest rate, facilities, loan-to-deposit ratio, total capital ratio, per capita income, inflation and population density are considered structural factors affecting the efficiency of banks.​ With the increasing improvement of technology and the change in the provision of banking services from traditional banking to electronic banking, there is intense competition between banks and other financial institutions. Also, most successful institutions are the ones that have lower costs and better efficiency. The discussions of efficiency started with the reviews and studies of  Debreu and copmans in 1951 and continued by Farrell in 1957. What is considered as an efficient financial system is a system that provides financial services with the accuracy and speed of operation at lower cost.
Methodology: The paper’s aim is to evaluate the efficiency and cost gap ratio of Islamic and conventional banks with an analytical-descriptive approach and examine the role of various factors in this analysis. Identifying the variables and ratios that affect the efficiency of banks is of great importance because it can improve the measurement of operational efficiency in banks.The method used in this research is to obtain metafrontier efficiency (including efficiency and cost gap ratio) of banks. In this study, efficiency is extracted from the Stochastic Frontier Analysis (SAF) method according to different financial groups and dividing them into Islamic and conventional banking groups, and the cost gap ratio is obtained from the metafrontier model. This paper is a parametric design and it is a combination of Stochastic Frontier Analysis and non-linear optimization. Thus, the efficiency and cost gap ratio for 50 Islamic banks and 50 non-Islamic (conventional) banks during 2013-2019 were calculated. The reason for choosing the countries investigated in the research (including Iran, Jordan, United Arab Emirates,   Indonesia, Bahrain, Bangladesh, Turkey, Pakistan, Tunisia, Iraq, Saudi Arabia, Oman, Philippines, Qatar, Kuwait, Malaysia and Egypt) is that The selected countries, except Iran, whose banking is 100% Islamic, have both types of banking systems (Islamic and conventional). Therefore, it is easy to compare them. Access to the statistical information of these banks has been obtained from the Bank Scope website and the Orbis database in cooperation with the Central Bank of the Islamic Republic of Iran.
Results and Discussion: It was found that inefficiency, cost gap ratio, interest rate, loan-to-deposit ratio and total capital ratio are observed more in Islamic banks than conventional banks and this difference is significant at the 99% probability level. The total cost, the price of fixed capital, facilities and the degree of money circulation are considerably higher in conventional banks than in Islamic banks. The labor price, per capita income, inflation and population density are not significantly different in the two groups. Based on the stochastic frontier cost function, the efficiency of Islamic banks during the years 2013 to 2019 was estimated. Saudi British bank JSC (THE) belonging to Saudi Arabia has the highest average efficiency among the investigated banks, the efficiency of this bank for the research period is 0.9390. Also, the lowest average efficiency rate of 0.2683 is dedicated to sarana multi infrastruktur, PT (PERSERO) bank in Indonesia As it was stated, al rajhi bank public joint stock company in Qatar has the highest average efficiency among the investigated banks, the efficiency of this bank is equal to 0/8927. Also, the lowest average efficiency of 0.3647 belongs to QIB Bank (UK) PLC in Qatar. The efficiency of other banks is also given and, Iranian banks have an efficiency of about 49 to 82 percent. Saudi british bank JSC (THE) in Saudi Arabia has the highest average efficiency among the investigated banks, the efficiency of this bank is equal to 0.9469. Also, the lowest average efficiency of 0.2710 belongs to sarana multi infrastruktur, PT (PERSERO) bank in Indonesia.
 Conclusion: In the results indicated that the inefficiency and cost gap ratio are higher in Islamic banks than in conventional banks. Therefore, the hypothesis that Islamic banks are more efficient cannot be supported.. In this regard, the lower efficiency of Islamic banks is also evident in all the years of the study. By examining the efficiency of different banks, the efficiency of Turkish banks (both Islamic and conventional groups) is higher than other countries. However, Iran has a weak position among different countries in terms of efficiency. It can be stated that some items such as not paying attention to the basic principles of Islamic banking, the lack of establishment of Islamic banking, the lack of communication with Islamic banks in other countries , intense competition, global sanctions, the weakness of monetary structural components , financial issues, structural weakness in creating a proper Islamic banking network, formality of most contracts and lack of attention to the basic nature of the Islamic economy, etc. are some of the important items.